ES2341109T3 - EXPANSIBLE GRANULATES OF STYRENE POLYMERS, WITH A BIMODAL DISTRIBUTION OF THE MOLECULAR. - Google Patents

Abstract

Expandable pelletized styrene polymer materials with at least bi- or multimodal molecular weight distribution, to a process for their preparation, and to use for producing moldable-foam moldings.

Description

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Expandable styrene polymer granules, with a bimodal or multimodal distribution of molecular weight.

The invention relates to expandable granules of styrene polymers with a distribution, at least bimodal or multimodal, molecular weight, to a procedure for obtaining and to the use to obtain pieces molded with foam in particle shape

They have known each other for a long time procedures for obtaining expandable polymers of styrene, such as expandable polystyrene (EPS) by means of the suspension polymerization. These procedures have the disadvantage that large amounts of water are formed residuals and these have to be removed. The polymers have to be dried in order to eliminate internal water. For other part, suspension polymerization leads, as a rule, to too wide distributions of pearl size, which they have to be screened expensively in various fractions of pearls

On the other hand, styrene polymers expanded and expandable have to be prepared by means of extrusion procedures In this case it is mixed in the fusion of polymer the propellant, for example by means of a extruder, is transported through an injector plate and is particle or macaroni granule (US 3,817,669, GB 1,062,307, EP-B 0126 459, US 5,000,891 as well as US 2003/0162852).

EP-A publication 668 139 describes a procedure for the economical obtaining of granules of expandable polystyrene (EPS), taking place to obtain the fusion containing propellant, by means of elements static mixers in a stage of dispersion, maintenance and cooling and then granulation is carried out. As a result of the cooling of the fusion to a few degrees above the solidification temperature it is necessary to carry a high heat dissipation.

In order to widely avoid the formation of foam after extrusion, various have been proposed procedures for carrying out granulation, such as granulation under water (EP-A 305 862), the spray mist (WO 03/053651) or spray (US 6,093,750).

Publication WO 98/51735 describes polymers expandable styrene, containing graphite particles, with a decreased thermal conductivity, which can be obtained by means of a suspension polymerization or by means of a extrusion in a twin screw extruder. As a consequence of high shear forces in a twin screw extruder, as a rule, a significant degradation of the molecular weight of the polymer used and / or a partial decomposition of the additives provided, such as protective agents Against the flame

In order to achieve properties of optimal insulation and good surfaces of material bodies foamed, the number of cells and the foam structure, which is established at the time of foam transformation of expandable styrene polymers (EPS) EPS granules, prepared by extrusion, cannot frequently foam into foamed materials  with an optimal foam structure.

The task of the present invention consisted of provide expandable styrene polymer granules with improved expansion skills. Material particles foamed, which can be obtained from said granules by prior foaming, they should also present a improved weld ability and should lead to bodies molded foam in the form of particles with a surface of plumed foam-free material.

Consequently, granules were found expandable styrene polymers with a weight distribution at least bimodal or multimodal molecular, in accordance with the claim 1.

Bimodal or multimodal weight distribution molecular can be adjusted, for example, specifically by means of mixing and melting styrene polymers with various average molecular weights. In this case mixtures are used constituted by a low molecular weight styrene polymer with a weight average molecular weight M w in the range between 1,000 and 20,000 g / mol, especially in the range between 2,000 and 10,000 g / mol and by a polymer of high molecular weight styrene with a molecular weight weight average M_ {w} located in the interval between 160,000 and 400,000 g / mol, preferably located in the range between 220,000 and 300,000 g / mol.

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The low molecular weight styrene polymer is used in amounts in the range of 0.1 to 30% by weight, preferably in the range of 1 to 10% by weight, based on the mixture of styrene polymers. Up to a proportion of 2% by weight of the polymers of the low molecular weight styrene, in relation to the mixture of the styrene polymers, a decrease worthy of consideration of the glass transition temperature of the expandable granulate of polymers of polymers of styrene and therefore

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An aptitude for expansion is achieved clearly enhanced with proportions of styrene polymer of low molecular weight in the range between 3 and 8% by weight.

In accordance with the invention, they are used mixtures consisting of

i)

from 0.1 to 30% by weight of a copolymer of styrene, for example of a copolymer consisting of styrene, acrylic acid and / or α-methylstyrene, with a weight average molecular weight M_ {w} located in the range between 1,000 and 20,000 g / mol, especially located in the range between 2,000 and 10,000 g / mol, Y

ii)

from 99.9 to 70% by weight of polystyrene ordinary (GPPS) with a weight average molecular weight M_ {w} located in the range between 160,000 and 400,000 g / mol, preferably located in the interval between 220,000 and 300,000 g / mol.

They are preferably employed as polymers of styrene transparent polystyrene (GPPS), resilient polystyrene (HIPS), polymerized polystyrene via anionic or resilient polystyrene (A-IPS), the copolymers of styrene-? -methylstyrene, the polymers of Acrylonitrile Butadiene Stirene (ABS), styrene-acrylonitrile (SAN), the acrylonitrile-styrene-acrylate (ASA), the methacrylate-butadiene-styrene (MBS), the methacrylate polymers of methyl acrylonitrile butadiene styrene (MABS) or mixtures thereof or with polyphenylene ethers (PPE).

The said styrene polymers may be mixed with thermoplastic polymers, such as polyamides (PA), polyolefins, such as polypropylene (PP) or polyethylene (PE), polyacrylates, such as polymethacrylate methyl (PMMA), polycarbonate (PC), polyesters, such as polyethylene terephthalate (PET) or terephthalate polybutylene (PBT), polyethersulfones (PES), polyether ketones or polyether sulfides (PES) or mixtures thereof in order to improve mechanical properties or stability against temperature, if appropriate with the use of compatibilizing agents, as a rule in total proportions of up to 30% by weight at most preferably in the range between 1 and 10% by weight, referred to the fusion of the polymers On the other hand, mixtures are also possible, in quoted quantitative intervals, also with, for example, polymers or with oligomers modified in a water-repellent manner or functionalized, with rubbers, such as polyacrylates or polydiene, for example block copolymers of styrene-butadiene or aliphatic copolyesters or biodegradable aliphatic / aromatic.

As compatibility promoters are suitable, for example, modified styrene copolymers with maleic acid anhydride, polymers containing groups epoxide or organilanes.

In the same way, they can contribute to fusions of styrene polymers, recycled materials polymers of said thermoplastic polymers, especially styrene polymers and expandable styrene polymers (EPS), in amounts such that they do not essentially worsen their properties, as a rule can be provided in quantities 50% by weight maximum, especially in quantities between 1 and 20% by weight.

The fusion of polymers of styrene containing propellants contains, as a rule, one or more propellant agents in a homogeneous distribution in a proportion total comprised between 2 and 10% by weight, preferably between 3 and 7% by weight, referred to the fusion of styrene polymers containing propellant agents. How propellants are suitable physical propellants which are usually used in the EPS, such as hydrocarbons aliphatic with 2 to 7 carbon atoms, alcohols, ketones, ethers or halogenated hydrocarbons. By way of preferably, iso-butane, the n-butane, iso-pentane, n-pentane

In order to improve training capacity foam, internal water droplets can be introduced finely divided into the styrene polymer matrix. This it can be carried out, for example, by adding water in the molten matrix of the styrene polymer. Water addition it can be carried out locally before, with or after the dosage of propellant agents. A homogeneous distribution of water can be achieved by means of dynamic mixers or static

As a rule, 0 to 1 is sufficient 2, preferably with 0.05 to 1.5% by weight of water, referred to styrene polymer.

Expandable polymers of styrene (EPS) with at least 90% of internal water, in the form of water droplets internal, with a diameter located in the interval between 0.5 and 15 µm, form, at the time of transformation into foam, foamed materials with a sufficient number of cells and with a homogeneous foam structure.

The amount of the propellant and the amount of water supplied is chosen in such a way that the polymers expandable styrene (EPS) have an ability to expand α, defined as bulk density before bulk foam / density transformation after transformation into foam with a maximum value of 125, so preferably between 25 and 100.

The expandable polymer granules of styrene (EPS), in accordance with the invention, present, by general rule, a bulk density of 700 g / l at most, of preferred manner in the range between 590 and 660 g / l. When loading materials are used, they may be presented bulk densities located in the range between 590 and 1,200 g / l depending on the type and quantity of the material of load.

In the same way, they can be contributed to additive styrene polymer fusions, forming agents Germs, fillers, plasticizers, protective agents against flame, inorganic and / or organic dyes and pigments, soluble and insoluble, for example IR absorbers, such as soot, graphite or aluminum powder together or separated in space, for example by means of a mixer or a side extruder. As a general rule, the dyes and pigments in amounts in the range between 0.01 and 30, preferably located in the range between 1 and 5% by weight. To carry out the homogeneous and microdispersed distribution of the pigments in styrene polymer it may be convenient, so especially in the case of polar pigments, use an agent dispersion aid, for example organosilanes, polymers that contain epoxy groups or styrene polymers grafted with maleic acid anhydride. Preferred plasticizers are those mineral oils, phthalates, which can be used in amounts between 0.05 and 10% by weight, based on styrene polymer.

To carry out the obtaining of the polymers expandable styrene, in accordance with the invention, is Mix the propellant in the polymer fusion. He procedure covers stages a) corresponding to the training of the fusion, b) corresponding to the formation of the mixture, c) corresponding to cooling, d) corresponding to transport and e) corresponding to granulation. Each of these stages can be carried out by means of devices or combinations of known devices for the transformation of materials synthetic To carry out the mixture, the static or dynamic mixers, for example extruders. The Polymer fusion can be removed directly from the polymerization reactor or can be formed directly in the mixer extruder or in a stand-alone mixer extruder by means of the fusion of the granules of the polymers. He fusion cooling can be carried out on the devices Mixers or in independent refrigerators. For granulation come into consideration, for example, pressurized granulation under water, granulation with rotating blades and the cooling by means of liquid spray mist heaters or spray granulation. The sets of appliances, which are suitable for carrying out the procedure are, for example:

to)

polymerization reactor - static mixer / refrigerator - granulator,

b)

polymerization reactor - extruder - granulator,

C)

extruder - static mixer - granulator,

d)

extruder - granulator.

On the other hand the set can present a lateral extruder to carry out the introduction of additives, for example of solid materials or additives thermally sensitive

The fusion of styrene polymers, which Contains propellant agents, is transported through the plate nozzles with a temperature in the range between 140 and 300 ° C, preferably in the range between 160 and 240 ° C. Cooling up to the interval of the glass transition temperature is not necessary.

The nozzle plate is heated at least until the melting temperature of the polystyrene containing the agent propeller. Preferably the temperature of the plate nozzles are in a range between 20 and 100 ° C above the temperature of the polystyrene melt that It contains the propellant. In this way, deposits of polymers in the nozzles and a granulation free of disturbances

In order to obtain granulate sizes suitable for commercialization, the diameter must be found (D) of the nozzle holes at the nozzle outlet in the range between 0.2 and 1.5 mm, preferably in the range between 0.3 and 1.2 mm, so especially preferred in the range between 0.3 and 0.8 mm In this way, sizes of the granulated below 2 mm, even after the expansion of the macaroni, especially in the range between 0.4 and 1.4 mm

Macaroni expansion can be influenced by the geometry of the nozzles besides being it by means of the molecular weight distribution. The nozzle plate features preferably holes with a U / D ratio of at least 2, designating the length (L) the area of the nozzle, whose diameter corresponds, at most, to the diameter (D) at the outlet of the nozzle. Preferably, the U / D ratio is found in the interval between 3 and 20.

In general, the diameter (D) of the holes in the nozzle inlet of the nozzle plate should be at least twice as large as the diameter (D) at the outlet of the nozzle.

An embodiment of the nozzle plate It has holes with conical entry and an angle of entry to less than 180º, preferably in the interval between 30 and 120º. In another embodiment, the nozzle plate It has holes with conical exit and with an exit angle β less than 90 °, preferably located in the range between 15 and 45º. In order to be able to generate specific distributions of the granulate size of the Styrene polymers, the nozzle plate may be equipped with holes with different outlet diameters (D). Likewise the various embodiments of the nozzle geometry.

An especially preferred procedure for carry out the production of expandable styrene polymers  With a bimodal molecular weight distribution, it covers the stages from

to)

polymerization of styrene monomer to give ordinary polystyrene (GPPS) with an average molecular weight located in the range between 160,000 and 400,000 g / mol,

b)

the degassing of the fusion obtained from styrene polymer,

C)

the mixture of a low weight styrene copolymer molecular weight with an average molecular weight M w located in the range between 1,000 and 20,000 g / mol,

d)

the mixture of the propellant and, where appropriate, of the additives, in the fusion of the styrene polymer by means of static or dynamic mixers at a temperature of 150 ° C as minimum, preferably between 180 and 260 ° C,

and)

the polymer melt cooling of styrene, which contains the propellant, up to a temperature which takes a value of at least 120ºC, preferably between 150 and 200 ° C,

F)

discharge through a nozzle plate with holes, whose diameter at the outlet of the nozzles takes a value 1.5 mm maximum and

g)

the granulation of the fusion containing the agent propeller.

In step g) the granulation directly behind the low nozzle plate water, at a pressure in the range between 1 and 25 bars, preferably between 5 and 15 bars.

As a consequence of the polymerization in the stage a) and degassing in stage b) is available directly from a polymer fusion for impregnation with the propellant agent in step d) and no fusion of the styrene polymers. This is not only cheaper but also leads to expandable styrene polymers (EPS) with low monomeric styrene content, since the effect is avoided shear mechanic in the fusion zone of an extruder, which generally leads to an inverse dissociation of the monomers In order to keep the styrene content low monomer, especially with styrene monomer contents by below 500 ppm, it is also convenient to keep as low as mechanical and thermal energy input is possible in all successive stages of the procedure. Therefore, in the stages d) to f) are maintained, especially preferably, shear rates below 50 / second, so preferably between 5 and 30 / second, and are maintained temperatures below 260ºC as well as times of short residence, located in the interval between 1 and 20, preferably between 2 and 10 minutes. By way of especially preferred, they are used in the whole procedure, exclusively, static mixers and static refrigerated The fusion of the polymers can be transported and unloaded by means of pressure pumps, for example by means of cogwheel pumps.

Another possibility to decrease the content in styrene monomer and / or in residual solvents such as the ethylbenzene, is to have in stage b) a high degassing by means of dragging agents, for example the water, nitrogen or carbon dioxide, or in carrying out the polymerization step a) anionically. Polymerization Styrene anionic not only leads to styrene polymers with a low proportion in monomeric styrene but, at the same time, leads to lower proportions of oligomers of the styrene

To improve the transformation capacity the expandable polymer granules of the styrene, finished, by means of glycerin esters, of antistatic or nonstick agents.

The expandable polymer granules of styrene, according to the invention, have a low stickiness against granules, which contain plasticizers of low molecular weight, and are characterized by a low loss of Pentane during storage.

The expandable polymer granules of styrene, according to the invention, can be subjected to a prior foaming, in a first stage, by means of hot air or water vapor to give foam particles with a density located in the range between 8 and 100 g / l and, in a second stage, can be welded in a closed mold to give pieces molded particles.

Examples Raw Materials

PS polystyrene 158 K of the BASF Aktiengesellschaft firm with an index of VZ viscosity of 98 ml / g (M w = 280,000 g / mol, heterogeneity M_ {w} / M_ {n} = 2.8),

PS polystyrene 138 F of the firm BASF Aktiengesellschaft with an index of VZ viscosity of 75 ml / g (M_ {w} = 195,000, M_ {w} / M_ {n} = 2.7)

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Copolymer of styrene (SC) consisting of styrene, acrylic acid and α-methylstyrene with a molecular weight weight average M_ {w} = 3,000 g / mol, transition temperature 56 ° C glass Tg (Joncryl® ADF 1300 from Johnson Polymers)

Examples 1-4

For the examples a fusion of polystyrene consisting of PS 158 K and SC polystyrene with the proportions by weight according to table 1 and an additionally mixed 6% by weight of n-pentane, referred to the fusion of the polymers The melt mixture, which contains the agent propellant, cooled from originally 260 to 190 ° C and transported with a flow of 60 kg / h through a nozzle plate with 32 holes (diameter of the nozzles 0.75 mm). They prepared compact granules with a narrow size distribution with help of pressurized granulation under water. In table 1 they have gathered the pentane contents measured in the granulate after of granulation and after 14 days of storage.

These granules were subjected to foaming water vapor precursor to form foam beads (30 g / l), were stored provisionally for 12 hours and at then they were welded in gas-tight molds with steam of water to give bodies of foamed material.

To carry out the welding evaluation material specimens were broken from foam particles foamed with a thickness of 4 cm and the proportion of the destroyed foam beads and non-destroyed beads in the breakage surface Breaking weld characterizes the pearl cohesion and therefore is a measure of the mechanical properties, such as bending behavior. The surface qualities were evaluated in the way it has met in table 1.

Table 2 shows the ability to expand the granules. With contents greater than SC it is clearly reduced The minimum bulk density and is achieved in a shorter time.

TABLE 1 Characterization and properties of examples 1 to 4

one

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TABLE 2 Ability to expand the granules from of examples 1 to 4 (bulk density [g / l])

2

3

Examples 5-7

The fusion of polystyrene, which contains the propellant (6% by weight of n-pentane) is extruded with a flow rate of 100 kg / h through a nozzle plate with 300 holes (diameter at the nozzle outlet (D) 0.4 mm). The melting temperature was 160 ° C. The expandable granules of polystyrene obtained had a unit diameter of the granulate with a value of 1.0 mm. The granules obtained were expanded to then with water vapor current and the expandability

4

Claims (5)

1. Expandable styrene polymer granules with a bimodal or multimodal molecular weight distribution, characterized in that they contain, respectively, the total proportion of the styrene polymer

i)

from 0.1 to 30% by weight of a copolymer of styrene with a weight average molecular weight M_ {w} located in the range between 1,000 and 20,000 g / mol, and

ii)

from 99.9 to 70% by weight of polystyrene ordinary (GPPS) with a weight average molecular weight M_ {w} located in the range between 160,000 and 400,000 g / mol

2. Expandable styrene polymers according to claim 1, characterized in that a copolymer consisting of styrene, acrylic acid and / or α-methylstyrene is used as the styrene copolymer. 3. Expandable styrene polymer granules according to claim 1 or 2, characterized in that they contain from 3 to 7% by weight of an organic propellant. 4. Procedure for obtaining granules expandable polymers of styrene according to claim 1, which understand the stages of

to)

obtaining a mixture of polymers from styrene, which contains, referred respectively to the proportion total in styrene polymers,

i)

from 0.1 to 30% by weight of a copolymer of styrene with a weight average molecular weight M_ {w} located in the range between 1,000 and 20,000 g / mol, and

ii)

from 99.9 to 70% by weight of polystyrene ordinary (GPPS) with a weight average molecular weight M_ {w} located in the range between 160,000 and 400,000 g / mol,

b)

the mixture of an organic propellant in the melting of the polymers by means of a static mixer or dynamic at a temperature of at least 150ºC,

C)

the cooling of the fusion of the polymers, which contains the propellant, up to a temperature of 120 ° C as minimum,

d)

discharge through a nozzle plate with holes, whose diameter at the outlet of the nozzles takes a value 1.5 mm maximum and

and)

fusion granulation, which contains the agent propeller, directly behind the nozzle plate, under water, at a pressure in the range between 1 and 25 pubs.

5. Method for obtaining particulate molded parts, characterized in that, in a first stage, they are subjected to prior foaming to the expandable granules of styrene polymers, in accordance with claim 1, by means of air hot or steam to form foam particles with a density in the range between 8 and 100 g / l and, in a second stage, are welded in a closed mold.